PROJECT SUMMARY Ischemia-reperfusion (IR) injury is implicated in a large array of pathological conditions in the retina including glaucoma, diabetic retinopathy, anterior ischemic optic neuropathy and traumatic optic neuropathy. Thus, understanding the events involved in ischemic neuronal injury can provide us with clinically effective treatments for many retinal diseases. Although the cause of this injury is multifactorial, increasing experimental evidence suggests an important role for the innate immune system in initiating the inflammatory cascade leading to detrimental/deleterious changes in retinal function. Toll-like receptors (TLRs) are recognized as one of the main contributors to pathogen-induced inflammation and, more recently, injury-induced inflammation. Endogenous ligands liberated from injured/necrotic cells can activate TLRs, initiating an inflammatory response even in the absence of pathogens. Our published results indicate that the level of endogenous ligands for toll- like receptor 4 (TLR4) increases in retinal IR and, through activation of TLR4, are involved in retinal damage and inflammation triggered by ischemic injury. Importantly, our preliminary results suggest that the mechanisms mediating ischemic damage in the retina are facilitated not only by inflammation induced by astrocytes, microglia, or infiltrating immune cells, but also by activation of TLR4 in retinal ganglion cells (RGCs) themselves. However, the exact mechanism of TLR4 signaling-induced inflammation and damage after retinal IR injury remains unknown. In this project we hypothesize that TLR4 signaling plays a significant role in the pathogenesis of retinal IR injury by directly and/or indirectly contributing to the injury of RGCs. This hypothesis will be tested in a series of experiments outlined in the following specific aims: 1) to determine whether TLR4 coordinates the immune response of the retina to IR injury~ 2) to determine whether silencing of TLR4 signaling reduces blood retinal permeability and infiltration of leukocytes in the ischemic retina~ 3) to determine whether TLR4-mediated signals directly injure RGCs~ 4) to define the role of TLR4 ligands in the post-ischemic retina. Completion of these specific aims could lead to the discovery of innovative strategies to help prevent the loss of vision in patients suffering from retinal ischemia, as selective targeting of both TLR4 and its ligands may be more effective for the development of therapeutic tools to prevent IR injury than targeting the intracellular pathways.